Electromechanical vibrator apparatus



Dec. 16, 1941. G. w. PIERCE 2,266,070

ELECTROMEGHANICAL VIBRATO APPARATUS Original Filed March 29, 1926 Gefolge Win-eroe AZ m Patented Dec. 16, 1941 ELECTROMECHANICAL VIBRATOR APPARATUS George Washington Pierce, Cambridge, Mass.

Original application Marc 98,220, now Patent No. 2

h 29, 1926, Serial No.-

,133,643, dated October 18, 1938. Divided and this application September 28, 1938, Serial No. 2

30 Claims.

'I'he present invention relates to electromechanical vibrators, and more particularly to piezo-electric crystals, and to supports and holders therefor. The present application is a division of application, Serial No. 98,220, filed March 29, 1926, which matured, on October 18, 1938, into Letters Patent 2,133,643.

Such vibrators, as is now well known, execute mechanical vibrations under vibratory electrical stimulus and, conversely, develop electrical po-l tentials as a result of their mechanical vibrations. Piezo-electric crystal bodies possess at least one, and usually two or more, axesknown as the electrical axes of the body-that have definite orientations in the original crystal. Quartz crystals have three such electric axes. Such bodies have, in general, a plurality of particular modes of mechanical vibration, of different frequency, corresponding to two or more of its dimensions. Among these are the longitudinal and the transverse modes of vibration. These mechanical and electrical effects are normally transitory, for the crystal body will not, of itself, persist in continuous vibration.

An object of the present invention is to provide an improved electromechanical vibrator. The improved vibrator of the present invention may be used for many purposes: for example, as a resonator, or to produce oscillations at very nearly constant frequency.

The frequency of vibration of electromechanical vibrators, like piezo-electric crystals depends upon the medium, such as air, in which they are disposed, and the temperature of that medium. Changes of the medium and of the temperature introduce frequency changes.

A further object of the invention, therefore, is to provide a new and improved holder for an electro-mechanical vibrator with the aid of which such frequency changes shall be obviated.

Other and further objects of the invention will be explained hereinafter, and will be pointed out in the appended claims, it being understood that it is intended to cover in the appended claims all the novelty that the invention may possess.

In the accompanying drawing, Fig. 1 is a longitudinal vertical section through a preferred holder for an electromechanical vibrator, comprising a piezo-electric body provided with electrodes in accordance with the present invention; Fig. 2 is a similar view of a modification employing a temperature bath; and Fig. 3 is a similar view of a further modification.

The preferred form of electromechanical vithe oppositely disposed sides or surfaces 4 and 6 of the crystal 2 being provided with opposed, conducting preferably fiat terminals, plates or electrodes 8 and l2, by means of which the crystal is adapted to be connected into an electric circuit. For high frequencies, it is necessary to use the period of the crystal determinedby a dibrator is illustrated as of the piezo-electric type,

mension of the specimen that is small compared to its other dimensions, as by its thickness, the crystal plate vibrating in the thickness mode. The thickness dimension is assumed, for concreteness, to be the dimension along one of the electric axes of the crystal, perpendicular to the electrodes 8 and l2, and this must be of the order of one millimeter for a frequency of 3000 kilocycles per second. The apparatus of the present invention may, however, be employed equally well at high and at low frequencies.

The invention is not, however, in its broader aspects, limited to such a crystal body, but may employ any body or mechanism having like proporties in itself, or like properties introduced by electric currents, electric polarization, magnetic fields, etc. 'lire vibrator may be a parallelopiped in shape, but it may be lenticular, as illustrated in the said Letters Patent, or it may be of any other shape, as a at disc, with rectangular, circular or irregular base. It may be constituted of any suitable substance having sufficiently pronounced piezo-electric properties. Quartz is preferred, because of its durability and constancy. The term electromechanical vibrator-or, more simply, the term vibrator-will be employed hereinafter in the specication and the claims to denote any substance or arrangement, whether or not crystalline in character, that is endowed with the above-referred-to property of changing shape or dimensions under the action of an electric force or an electric current and of reacting on the electric circuits.

In. Fig. 3, the electrode 8 is shown constituted of a flat bottom or base plate of a metal box, container or housing l0, within which the vibrator 2 is centrally located, as shown. The electrode l2 here takes the formof a metal spring member that positively and intimately contacts with the upper surface 6 of the crystal 2. The

spring member is electrically connected to plug binding postsll by a screw I9. This construction renders the electrical connection of the vibrator to its binding posts resilient. The spring pressure is, of course, made very light, so as not to press so heavily upon the vibrator as to interfere with its' free vibration. The plugs Il are provided with longitudinally extending spring a minimum.

angers 45 that are adapted to press outward against the inner walls of sockets (not shown) to of the crystal, and the top wall of the housingA I may, in both cases, be integral with the base of the-housing I0. The side or surface 4 of the vibrator is shown, in Fig. 3, engaging the electrode 8, and the opposite side or surface 6 may contact with, or may be near to, the electrode I2. In Fig. l, the crystal is shown entirely free of and spaced from the electrode I2. In Figs. 1 and 2, the crystal is thus shown secured freely in the casing or housing I0 between the electrodes 8 and I2 without being in any way restricted, so that it is free to vibrate mechanically between the opposed electrodes 8 and I2, according to any of its. modes or periods of natural vibration or any of its overtones of such modes of vibration.

In Fig. l, the electrode 8 is shown electrically connected to a lead I4, and the plate I2 to a lead.

I6 suspended over the crystal 2. Electrical connectlon is thus established between the two sides 4 and 6 of the crystal and the leads exterior of they housing.

In Fig. 3, the cracks 25 between the side walls and the cover member I8 and the cracks 29 between the binding post or 'posts I'! and the insulating members upon which they are mounted may be sealed by Celluloid varnish, wax or other coating to seal the receptacle |10 hermetically to the atmosphere. To attain great constancy of frequency, the housing may be evacuated so as to remove air or other gas and thus eliminate air-column resonance which, by its variation with 'temperature, introducessmall changes of frequency. The vibrator becoming thus hermetically closed in the housing, it is further protected from the action of moist gases,

` dust and the like.

The evacuation of thevesseL if carried to a high degree, will prevent the formation of corona which, by electronic action and heating, may produce disintegration and breaking up of the crystal. 1

In the modification of Fig. 2, there is disclosed a crystal holder more particularly adapted.

for use for frequency standards, in which the crystal vibrates in the direction of its length. The electrode ||2 is provided with an intermedijections and |22 over or at medial areas that are relatively smallcompared to the dimensions of the vibrators. These medial areas correspond, therefore, to diametrically oppositely disposed medial nodal zones of movement of the crystal. When the crystal is vibrated transversely in the direction of the medially disposed electric axis, a node of motion, where there is small vibratory movement of the crystal, is produced at these relatively small nodal areas. Damping of the crystal is, by this construction, thus reduced to The electrodes |08 and ||2, with together as a unit between two insulating members ||8 by bolts |24. The whole is mounted in an evacuated sealed vessel of metal or glass.- A glass vessel |28 is shown in Fig. 2, the evacuation of which may be effected through an integral glass tube |42. The sealed vessel, whether of metal or glass, may be kept in a constanttemperature bath, as illustrated in Fig. 2.

It win be understood that the invention is not restricted to the exact embodiments thereof that `are illustrated and described herein, as modincations may be made by persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

l. Apparatus of the character described comprising an evacuated receptacle, means for maintaining the receptacle at constant temperature, and an electro-mechanical vibrator contained in the receptacle.

2. A piezo-electric crystal arranged for longitudinal or transverse vibration, the electrodes being spaced slightly apart from opposite faces of the crystal, and gripping means being jammed between the electrodes and the faces 'of the crystal near the middle of the length of the crystal or other nodal zones, the crystal, the electrodes and the gripping means being mounted in an evacuated vessel.

3. A piezo-electrical crystal apparatus comprising in combination a mounting, a piezoelectric crystal loosely held on the mounting, an evacuated, sealed housing surrounding said mounting, and an electrical connection with the i said piezo-electric crystal through the housing.

4. In'a piezo-electric crystal apparatus, the combination of a mounting, a piezo-electric crystal loosely secured on said mounting, and an evacuated housing around said mounting terminals extending outwardly from within said housing for establishing electrical connection with said mounting.

5. A piezo-electric crystal holder comprising, in combination, an evacuated sealed closure and means Within said closure for securing a piezoelectric crystal therein and establishing electrical connection therewith while permitting the free vibration of said piezo-electric crystal. Y

6. A crystal oscillator of the class described comprising a crystal and means surrounding the crystal to prevent a corona discharge thereon when the crystal oscillates.

7. A crystal oscillator of the class described,

comprising a container having a vacuum therein, and a crystal arranged within said container.

8. A crystal oscillator of the class described comprising a vessel, vand a crystal in the vessel, said vessel having a vacuum therein to prevent a corona discharge on the crystal during oscillation thereof. y

9. A crystal oscillator of the class described comprising a vessel, a crystal, and means to support the orysan within the 'vessel said vessel having a high vacuum therein. s A

10. A crystal oscillator of the class described comprising a vessel, a crystal in the vessel, and means to cause said crystal to vibrate, said vessel having a vacuum. therein to prevent an electrical discharge on the crystal.

11. As an article of manufacture, a crystal os- I' cillator comprising a vessel having a vacuum the crystal disposed between them. are clamped ei'tles mounted in the vessel.

, and terminals through the walls 12. In a device of the character described, a piezo-electric crystal mounted in a vacuum.

13. In a devce of the character describedl an oscillating crystal mounted in a vacuum.

14. In a device of the character described, an oscillating crystal and protective means surrounding the crystal to prevent a corona discharge thereon from the plates of the crystal which has a tendency to heat the crystal and make it break.

15. A piezo-electric crystal holder comprising in combination a base, an evacuated, sealed housing secured to said base, means for locating a piezo-electric crystal within said housing, and means for establishing electrical connection with the said piezo-electric crystal to a point outside of the housing. y

16. A piezo-electric crystal holder comprising in combination supporting members, an evacuated housing surrounding the supporting members, a piezo-electric crystal carried by said supporting members and electrically connected with the 'opposite ends of said holder and means whereby said piezo-electric crystal may be electrically connected in a circuit established through electric leads through the housing.

17. A piezo-electric crystal holder comprising in combination an evacuated sealed container, a piezo-electric crystal centrally positioned in said container, and means for establishing an electrical connection with said piezo-electric crystal within said container for permitting free vibration thereof. v

18. A receptacle for a piezo-electric crystal comprising in `combination an evacuated and sealed housing, an element capable of mechanical vibration mounted within said housing of said housing connected with the opposite faces of said element, said element being supported for permitting free mechanical vibration thereof.

19. A piezo-electric crystal holder comprising an evacuated closure, a pair of separated metal supports supported within the closure, a piezoelectric crystal loosely held between the metal supports, and an electrical connection to each metal support, and communicating with the out- 20. A piezo-electric crystal holder comprising an evacuated closure, a pair of separated metal plates supported within the closure, a piezoelectric crystal loosely held between the plates and an electric connection to each plate communicatlng with the outside ofthe closure.

21. A piezo-electric crystal holder -comprising in combination a hermetically sealed vitreous vessel and means within said vitreous vessel for securing a piezo-electric crystal therein and establishing electrical connection therewith to said crystal through said vitreous vessel, while permitting the free vibration or said piezo-electric crystal with substantially no restriction, the sptge within said vitreous vessel being evacua 22. A piezo-electric oscillator having in comin combination a support, an evacuated vessel secured to said support, means for supporting a piezo-electric crystal within said evacuated vessel, and means for establishing electrical connection with the said crystal from points on said support which are exterior to said vessel.

-24. A piezo-electric crystal holder comprising in combination a hermetically sealed closure and means within said closure for Securing a piezoelectric crystal therein and establishing electrical connection therewith, while permitting the free vibration of said piezo-electric crystal with substantially no restriction, the space within said closure being evacuated.

25. A piezo-electric oscillator having in combination a hermeticallytsealed vessel, a piezoelectric crystal therein, means within said vessel `:for mounting said crystal, and electrical connections lfor said crystal extending through said vessel, the space within said vessel being evacuated.

26. A piezo-electric oscillator having in combination a piezo-electric crystal, a mounting therefor, an evacuated housing surrounding said crystal and an electrical connection for said piezo-electric crystal extending through said housing.

27.A piezo-electric crystal apparatus comprising an electrode, a crystal resting on said electrode,'a second electrode spaced from the crystal, and a vitreous evacuated envelope surrounding said electrodes and crystal.

28. A piezo-electric crystal holder comprising in combination a hermetically sealed bulb and means within said bulb for securing a piezo-electric crystal therein and establishing electrical connection therewith to said crystal through said bulb, while permitting the free vibration of said piezo-electric crystal with substantially no -restriction, the space within said bulb being evacuated.

29. A piezo-electric oscillator having in combination a hermetically sealed bulb, a piezo-electric crystal therein, means Within said bulb for mounting said crystal and establishing electrical connection therewith, electrical connections extending through said bulb to said mounting, the space within said bulb being evacuated.

30. A crystal oscillator of the class described comprising, in combination, a closure and means within said closure for securing a piezo-electric crystal therein and establishing electrical connection therewith, while permitting the free vibration of said piezo-electric crystal with substantially no restriction, the closure being evacuated and sealed to prevent a corona discharge on the crystal when the crystal oscillates.

GEORGE W. PIERCE. 

